Plant water relations and growth of cowpea cultivars subjected to varying degree of waterlogging

There is potential in tropical regions to include cowpea (Vigna unguiculata (L.) Walp.) in rice (Oryza sativa) based cropping systems especially during the post-monsoonal dry season. The plant water relations and root and shoot growth of two cowpea cultivars (IT82D-889 early maturing and TVX1948-012F medium maturing) were compared in saturated and drier soil moisture regimes on an isohyperthermic clayey Typic Tropudalf soil by using a line-source sprinkler differential irrigation system. Saturated soil reduced total dry matter accumulation plant height crop growth rate and leaf area index by 20 to 50% 7 to 10% 20 to 50% and 20 to 30% respectively. Root length density (RLD) measurements showed that in saturated soil roots of both cultivars were concentrated in the top 0.1 m during the vegetative stage but in the reproductive stage grew down to 0.8 m. Leaf water potential (LWP) was higher by 0.3 MPa and conductances were higher by 5 to 29% in dry than saturated soil. The cultivar TVX1948-012F had greater RLD conductance and LWP than did with IT82D-889 under saturated conditions. Results suggest that the medium-maturing cultivar is better adapted than the early-maturing to high rainfall and high water table conditions in the post-rice environment. Its shallow rooting under saturated soil conditions enables more effective oxygen uptake in the vegetative growth phase. Deep rooting provides for effective water uptake and increased plant water status under subsequent drought conditions in the reproductive growth phase.

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